Power management architecture based on micro/processor architecture with embedded and external nvm

ABSTRACT

A control unit for power supply circuits of points of load (POL) of an electronic system includes a means for autonomous customization by the customer-user of the original control program residing in the ROM of the device, as well as configuration of control parameters of the POL. Microprocessor architecture of the device includes a dedicated logic block and a rewritable non-volatile memory coupled to the data bus of the device or to an auxiliary bus thereof, thus providing a means for software extension of the power supply circuits. RAM is loaded at start-up with data of modified or added routines for implementing new commands and values of configuration and control data of the POL. The RAM may optionally be subjected to encryption/decryption for protection. During operation, program execution jumps from ROM address space to RAM address space and vice versa when certain values of a program counter are reached.

BACKGROUND

1. Technical Field

The present disclosure relates in general to control systems of thepower supply of complex electronic systems and in particular to a methodof controlling a plurality of voltage regulators for as many load pointsof the system.

2. Description of the Related Art

A digital system for managing the power supply of complex electronicsystems, briefly a PMU, acronym for Power Management Unit, is a digitalunit adapted to manage programming, control, and telemetry of numerousvoltage regulators deployed as load points of the electronic system(briefly POL, acronym for Point Of Load) associated thereto. Eachvoltage regulator or POL may include a serial digital interface, atleast one synchronizing signal, a clock signal, a data transfer signal,and data signals to the PMU for accomplishing its tasks.

Implementation of the PMU consists today in a description of commands(COMMAND) customized to a specific POL that is identified with anaddress (ADDRESS). The serial digital interface may be proprietary(e.g., AMD and Intel) or complying to a published standard thatspecifies the electrical characteristics (e.g., SMBus.org). Thedescription of the commands, depending on the vendor, may also beproprietary or they may conform to an international standard (e.g.,PMBUS.org).

Nevertheless, Server developers, which on one hand have participated inthe definition of the standard, may consider a core set of commands andfunctions indispensable but not sufficient to their own specificationsand therefore the developers may add to the list of commands or to thePMBUS.org standard, specific proprietary additional commands of theirsystems and know-how.

A Power Management (PMU) commonly includes the set of commands andfunctions compliant to the International PMBUS.org standard and theirspecific added commands. The transmission of commands takes placeaccording to the PMBUS protocol and is based on the physical layer ofthe SMBUS.org standard, and every command sent by the System Controllercorresponds to an execution procedure of the standard.

In order to offer to the Server developers the possibility of extendingthe PMBUS commands while protecting the know-how and flexibility ofdeveloping to their software the particular requisites of their system,the adopted solution passes from a rigid hardware-type Power Managementunit (PMU), to a microprocessor architecture. However, by cost concern,conventional PMU CMOS fabrication processes do not offer the possibilityof implementing a re-writable nonvolatile memory (EEPROM or FLASH) forcontaining data for executing the commands.

A power management architecture having a PMU for each POL, connectedthrough a serial interface, is common today and described in the U.S.Pat. No. 7,000,125 (POWER-ONE, INC.) and schematically depicted in afigure of the published patent, herein reproduced as FIG. 1.

A PMU as described in the above mentioned document does not rigidlydefine an extended protocol with a set of redefined commands, but itdoes so only in a generic form in order to perform “programming” and“monitoring” of the functions of the PMU. In practice, a whole copy ofthe program would be necessary in RAM for permitting a re-write of partof the program to correct/adapt it to the peculiarities and necessity ofone system.

A known technique, referred to as “Patch Manager,” is normally appliedto digital systems for catching and processing images, wherein thecontrol application is normally executed by a microprocessor. U.S. Pat.No. 5,938,766 (APPLE COMPUTER, INC) is an example. According to thistechnique, in order to avoid using a RAM that is large enough to containthe entire program, the program is written in a way that it may bedivided into numerous routines that are stored in ROM. This techniqueintroduces the possibility of correcting the program executed by themicroprocessor without entirely copying the program code from the ROMwherein it resides to the RAM associated with the microprocessor. Aportion of the ROM contains the addresses (or symbols) of each routineof the program. The Patch Manager is aware of the set of addressescontained in ROM. At start, the Patch Manager will copy the set ofaddresses (pointers) to a predetermined RAM location to provide accessto the routine of the program in ROM. For example, if a first routine inROM needs to call a second routine in ROM, rather than directingexecution of the program to the ROM address of the second routine, thefirst routine will access the predetermined address in RAM of thepointer to the second routine. Therefore, the pointer to the secondroutine in RAM redirects the execution to the ROM address of the secondroutine. An implementation of a technique of Patch Manager used in othertechnical sectors is found, for example, in U.S. Pat. No. 5,938,766(Apple). In the example, the customer-user would find it impossible tocorrect any procedure that implements a vendor command different fromthose in the Power Management standard (e.g., PMBUS.org standard)without the values of the related parameters having been registered inan internal NVM and as such readable.

These related parameter values are often sensible data thatqualify/disclose crucial information of the client-user technology. Theexample technique offers economic advantages by avoiding the need of avery large RAM, which is often not acceptable by the customer-user.Furthermore, in mixed signal silicon technology, the usage of large RAMis a relevant cost. That is, by reducing the size of RAM, a competitiveadvantage versus similar products in the same market field can beachieved.

BRIEF SUMMARY

To address the inconveniences discussed above, which include limitationsand costs to implement control systems of supply voltage regulatorsemployed at numerous points of load (POL) in a complex electronic systemaccording to the conventional technique, the applicant has found aneffective solution. Embodiments of the effective solution do not requirethe loading in RAM of the whole program to introduce corrections,modifications, and/or adaptations to the peculiar characteristics andmeans of one's electronic system. Embodiments also do not require acomplete understanding of the communication or specific data of one'stechnology.

Embodiments of the novel technique include a Power Management Unit (PMU)that recognizes ADDRESS values and COMMAND values contained in a serialcommunication and, upon recognition of said values, the PMU executes aspecific procedure of programming, control, or monitoring of thecorresponding POL.

Microprocessor architecture offers remarkable advantages of flexibilityand reduced design risks. Microprocessor architecture also permits adesigner to create a dedicated logic block using a fast, re-writablenon-volatile memory (NVM) external to the PMU device. Embodiments of thepresent techniques can include an internal dedicated logic block and anexternal memory formed as a real PMU_EXTENDER.

Besides eliminating the need of sharing certain information with thevendor, the extension can be customized entirely with a design by thecustomer-user. The design, which in some embodiments is downloaded onthe external memory (for implementing the functional PMU_EXTENDER), mayoptionally contemplate data cryptation, thus avoiding the risk thatsensible information on the electronic system is accessible.

For implementing this function, an encryptioning algorithm and/or anError Correcting Code (ECC) key may be used. The encryption and/or ECCkey conform to the data format of the extension downloaded from theexternal NVM, which will coincide with that implemented in the hardwaredesign. In practice, even if a malware should know the hardwareimplementation, it will not be able to reach the firmware because itcould not recognize that the extracted bytes represent Assembler code ofa target CPU (e.g., INTEL CORPORATION 8051). To this end, the externalNVM will have an access key to the device in order to enable the ECCcontrol without which the download would not succeed. This key may bewritten in the internal NVM (which a hardware user could insert with therespective GUI), and which will coincide with the key recorded in theexternal NVM.

An encryption algorithm can greatly enhance protection. The encryptionalgorithm can be implemented in ROM and enabled or disable, and thepresence of the algorithm may or may not be publicized by themanufacturer of the integrated device.

Custom extensions may thus be managed by the same user of a system thatnormally uses a file of symbols extracted from the ROM. For example,where the symbols are inserted at the moment of developing the program(i.e., where a table of symbols that includes at least the names and ROMaddresses of the routines of the original program is generated), thetable of symbols may also contain a number of added symbols capable ofcopying into RAM as many routines as are adapted or modified by theuser. The Patch Manager can update the table of symbols for connectingan extension by modifying the program pointer. After updating the tableof symbols the Path Manager may be removed, and the PMU system canfunction with the introduced extension in a normal manner.

Embodiments of the invention are defined in the annexed claims, whichare intended to constitute subject matter of the present description andherein incorporated by expressed reference.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments are described with referenceto the following drawings, wherein like labels refer to like partsthroughout the various views unless otherwise specified. One or moreembodiments are described hereinafter with reference to the accompanyingdrawings in which:

FIG. 1 is a basic schema of a PMU based on the use of a microprocessorof prior art as already discussed.

FIG. 2 shows the basic schema of an embodiment of the PMU of the presentdisclosure.

FIG. 3 shows the enabling schema of the logic block PMU_EXTENDER atsystem start-up.

FIG. 4 is a basic schema of an embodiment of the PMU of the presentdisclosure.

FIG. 5 is an exemplary basic circuit diagram of the logic blockPMU_EXTENDER.

FIG. 6 shows a diagram implemented by the PMU of FIG. 4

DETAILED DESCRIPTION

The strictly functional schema of FIG. 2 shows a generic sampleimplementation of a power management control unit (PMU) for supplyvoltage regulator circuits of one or many points of load (POL) of anelectronic system, according to the disclosure. The fundamental elementsof the embodiment of FIG. 2 include an integrated device containing amicroprocessor (μC), in the considered example an 8051 CPU, system's RAMand ROM, the first logic circuit block SMBUS, a second logic circuitblock PMU_EXTENDED, an internal microprocessor data bus and an interfacecircuit SERIAL_INTERFACE configured to make available the digital datafrom a rewritable non-volatile memory NVM to the CPU resources.Optionally the PMU may also include the rewritable non-volatile memoryNVM, accessible by the device via said serial interface.

In more detail:

μC: is a microprocessor constituting the art of system, which acts upona serial communication of the external data bus of the microprocessor,the serial communication having an ADDRESS value and a COMMAND value.When the ADDRESS and COMMAND values are valid and received by the logicblock SMBUS, the μC executes the corresponding task or procedure.

SMBUS: is a logic circuit block that implements a logic function thattranslates a serial communication in byte packages. In one embodiment,for example, the logic block implements functions for the data layer ofan International Standards Organization (ISO) protocol. In such anembodiment, the physical layer may be a trivial protocol (e.g., aPHILIPS ELECTRONICS N.V. I²C protocol), the packet structure compliantto the SMBUS.org specification, and the command layer a PMBUS.orgprotocol. The logic block SMBUS operates such that the byte packages arevalidly received by the microprocessor. The method with which themicroprocessor receives the information may be dependent on the type ofmicroprocessor and/or the architecture of the software executed by themicroprocessor.

In one example, a condition of a valid ADDRESS value takes place in thelogic block SMBUS. The logic block SMBUS releases an interrupt (IRQ) tothe microprocessor that allows it to use the COMMAND as a pointer in alist of valid COMMAND routines. For each command, the microprocessorexecutes a . . . procedure of a routine, which represents an action tobe carried out.

RAM: is a random access memory accessible by any type of microprocessorand used to temporarily store the data of a software program. Possibledata may include the program itself, for example specific routines inwhich a whole program could may be divided. The connection of the RAM tothe μC may be implemented with a suitable data bus or with a shared bus.

ROM is a dedicated read only memory containing data such as the softwareprogram executed by the microprocessor. The microprocessor steps throughexecution of the program through a counter called Program_Counter.

NVM: is a rewritable non-volatile memory used, for example, incommercial devices of the prior art where such devices commonly storeparameters necessary to the programming and configuration of the POL. Inembodiments according to the present disclosure, an NVM may optionallybe present for the same purpose, in which case the NVM is a nonessential feature.

PMU_EXTENDER: is a circuit block adapted to implement a function thatmakes possible a correction of a part or all of the program codecontained in ROM to be executed by the microprocessor. In the context ofthis disclosure, the PMU_EXTENDER is arranged for modifying and/orincreasing the number of COMMAND routines that may be executed by thePMU. The PMU_EXTENDER function includes recording in RAM two logictables: one representing values of the Program_Counter coincident withinstructions making a jump in the address space of the ROM towardcorresponding addresses in RAM and vice versa; the other representingcontent in RAM that substitute, at that point of execution, the programcode residing in ROM.

SERIAL_INTERFACE enacts the coupling with an external peripheralintegrated device.

NVMext is an external rewritable non-volatile memory storing the twotables.

Preferably, hardware programming may be implemented at system start-up(Boot), at the search (“Patch Enable”) function of the external memoryNVMext, through the serial interface (which may not necessarily be anI²C protocol for a Serial Peripheral Interface (e.g., MOTOROLA SPI)protocol, or for some other protocol). The logic function of the serialinterface translates from serial to bytes the information gathered fromthe external memory NVMext.

Optionally on enhanced protection, the translated data could be subjectto encryption to prevent that information on one's system from beingusefully extractable from the NVMext. In such a case, the logic functionimplemented by the PMU_EXTENDER may include a decryption key written inROM or externally provided, for example through the logic block SMBUS.If the size of the RAM allows it, even the second table maybe completelydownloaded in RAM or, on the execution of the procedures of the softwareprogram code of each command, be downloaded from the external memory NVM“in distinct pieces” when necessary.

As schematically depicted in FIG. 3, if the external memory NVM isfound, its content is downloaded in RAM, including the two tablesdescribed above, and the PMU is arranged to carry out the adaptations orextension on the commands executed by the PMU.

EXAMPLE

With reference to the schema of a possible embodiment of FIG. 4, atstart-up, the logic function of the block PMU_EXTENDER is enabled. Anexemplary basic circuit in FIG. 5 depicts a scheme through which twotables are serially downloaded from an external memory NVMext. Theserial path, together with data from the external memory which istranslated in bytes, fills the pointer table XRAM_Pointers and theextension table XRAM Extensions in a predetermined order. The extensiontable XRAM_Extensions represents the program code written by thecustom-user which is executed for correcting or extending the PMBUScommands towards the respective POL.

Downloading of data from the external memory NVMext maybe subject to anintegrity check of data (parity bit, sum check) and to encryption.

The data of the tables are optionally released after integrity controland decrypting have been tested. The data stream at start-up isindicated with a hatched line in the schema of FIG. 4.

When the microprocessor μC executes a program, the program code isdownloaded from the ROM, and the pointer to the memory containing theprogram data is updated. The pointer “Program_Counter” is illustrated inFIG. 4 as pointing to the ROM in case the program resides only there,however, the pointer can point to both ROM and RAM in case the twomemories share the same address space.

A table of pointers XRAM_Pointers is in practice the list of addressesof the program memory (e.g., ROM alone or ROM and RAM) from which theProgram Counter redirects the execution (jumping address) and to whichthe Program Counter continues execution of the program (returningaddress). The list of addresses of the program memory XRAM Extension arepointers to which the Program_Counter is directed.

When the system controller senses and optionally verifies a PMBUScommand, the SMBUS peripheral controls the ADDRESS, passes the serialtransmission of the byte of the respective command COMMAND, andgenerates an interrupt IRQ to the microprocessor (μC).

The microprocessor uses the command information as a program pointer(Program_Counter_μP) for executing a routine corresponding to thereceived command. The PMU_EXTENDER compares the program pointer(Program_Counter_μP) with the table of pointers XRAM_Pointers in theJumping Address list. If the PMU_Extender does not find a matchingaddress, it leaves the Program_Counter remaining unchanged. The executedroutine is effectively the original (the routine present in ROM) and theProgram_Counter_μP is incremented upon evolution of the microprocessorClock.

If the PMU_Extender finds a match with a jumping address, it loads theProgram_Counter with the Returning_Address and therefore redirects theexecution of the program, for example from an extension routine copy inXRAM_Extensions. The Program_Counter is incremented upon evolution ofthe microprocessor Clock.

According to the possible embodiment, the Program_Counter_μP may be setto a new value of the Program_Counter, which was set by thePMU_EXTENDER. The Program_Counter_μP is set by inserting data in thedata stream from the RAM/ROM, which reaches the microprocessor. That is,the microprocessor executes in the program (Instruction Data), aninstruction of Jump to the address given by the Returning Address. Thiswill force the Program_Counter to said Returning Address.

The Jump instruction is common in every microprocessor; and isconsidered in an example embodiment (e.g., a 8051 microprocessor). Inthe example, the Jump instruction includes one byte and the memoryaddress to jump to includes two bytes. Therefore the PMU_EXTENDERintroduces three bytes in the instruction data in order to force theProgram_Counter.

The mechanism allows a user to modify some routines of commands or toadd new routines. That is, the user can add a new command not present inROM of the commercial device, (i.e., a command where theProgram_Counter_μP does not have any physical correspondence in ROM). Inthis case, the extension will have a jumping address toward a routinepresent in RAM at the location identified by the Returning Address.

It is also possible to substitute even a single program instruction suchas the attribution of a certain value to a variable.

For example consider addresses from 100 to 500 as address spaceaccessible by the Program_Counter in ROM and consider addresses from1000 to 2000 as the address space of extensions in XRAM_Extensions.Further consider the pointer table being loaded with the followingvalues: 150/1100; 1200/152. Then consider the case where the systemcontroller sends a PMBUS command number 127.

The μC loads the Program_Counter_μP with the value 127. TheProgram_Counter _μP and the Program_Counter coincide and both areincremented by the evolution of the CLOCK.

When the Program_Counter_μP=150, the PMU_EXTENDER loads theProgram_Counter with the value 1100.

The program is executed by the RAM from the location 1100 and theProgram_Counter evolves with the CLOCK until reaching the value 1200. Atthis point, the PMU_EXTENDER detects the value 152, redirecting theexecution of the program back into ROM. In practice, two instructions ofthe μC in ROM (the 150 and 151) are substituted with 100 instructions inRAM (from 1100 to 1199).

FIG. 6 shows the flowchart implemented by the PMU of FIG. 4.

The various embodiments described above can be combined to providefurther embodiments. The embodiments may include structures that aredirectly coupled and structures that are indirectly coupled viaelectrical connections through other intervening structures not shown inthe figures and not described for simplicity. These and other changescan be made to the embodiments in light of the above-detaileddescription. In general, in the following claims, the terms used shouldnot be construed to limit the claims to the specific embodimentsdisclosed in the specification and the claims, but should be construedto include all possible embodiments along with the full scope ofequivalents to which such claims are entitled. Accordingly, the claimsare not limited by the disclosure.

1. A control unit for supply voltage regulating circuits of one or morepoints of load of an electronic system, comprising: a microprocessor; arandom access memory (RAM) configured to temporarily store dataassociated with the execution of a program by the microprocessor; a readonly memory (ROM) configured to store data of an original softwareprogram of the control unit, the original software program executable bythe microprocessor according to instructions sequenced with a programcounter; a serial communication interface configured as a peripheral tothe microprocessor; a first logic circuit block adapted to translatepackets of serial data, the packets of serial data including operativeinformation transmitted to the microprocessor; a rewritable non-volatilememory coupled to the control unit via an internal bus, the rewritablenon-volatile memory configured to store data of a substitute softwareprogram to replace data of said original software program, thesubstitute software program configured to add or modify at least one of:a command executable with an associated software procedure initiated viaa communication protocol of the control unit between a supply voltageregulating circuit of a point of load and a microprocessor, and aprogramming parameter arranged to configure a respective supply voltageregulating circuit of a point of load; and a second logic circuit blockadapted to copy into a table in RAM said substitute software programdata configured to add or modify at least one of a command and aprogramming parameter, said second logic block further adapted toimplement a jump from address space of said original software program inROM toward an address in said table in RAM or vice versa when theprogram counter reaches a certain value.
 2. The control unit of claim 1,wherein at start-up of the electronic system, said second logic circuitblock is arranged to write two logic tables in said RAM: one tablerepresenting values of the program counter which effect a jump from theaddress space in ROM towards a corresponding RAM address and vice versa,and the other table representing addressable content of the substitutesoftware program at a point of execution of the original softwareprogram residing in said ROM.
 3. The control unit of claim 1, whereinextension data downloaded to said rewritable non-volatile memory isformatted according to a formatting implemented in a hardware design ofthe control unit, and said rewritable non-volatile memory is configuredto store a control unit access key adapted to enable an integrity check,the control unit access key identical to a key written in a secondinternal rewritable non-volatile memory.
 4. The control unit of claim 1,wherein at least some data contained in said rewritable non-volatilememory is encrypted and said second logic block includes a decryptionkey written in ROM or provided to the control unit via said first logicblock.
 5. The control unit of claim 2, wherein said second logic circuitblock includes a hardware programming circuit adapted to enable a searchof said rewritable non-volatile memory via said serial communicationinterface at start-up of the electronic system, the hardware programmingcircuit further adapted to copy the two logic tables into RAM.
 6. Thecontrol unit of claim 1, wherein the serial communication interfaceconforms to a data layer of an ISO protocol, a physical layer of an I2Cprotocol, or a command layer of PMBUS.org protocol.
 7. A powermanagement unit extender module, comprising: a microprocessor interface,the microprocessor interface including a program counter input and aninstruction data output wherein a microprocessor coupled to themicroprocessor interface is configured to serially receive powermanagement transaction information including an address value and acommand value; a memory interface configured to provide access to atable of jump values, an original software routine executable by themicroprocessor, and a substitute software routine executable by themicroprocessor; comparing logic configured to compare a power managementjump value from the microprocessor to at least one value in the table ofjump values; a power management unit extender program counter configuredto sequence through instructions of the original software routine andthe substitute software routine, wherein the power management unitextender program counter is configured to sequence through instructionsof the substitute software routine when the comparing logic detects amatch between the power management jump value from the microprocessorand a value in the table of jump values, and the power management unitextender program counter is configured to sequence through instructionsof the original software routine when the comparing logic fails todetect a match between the power management jump value from themicroprocessor and any values in the table of jump values, themicroprocessor interface configured to pass the sequenced instructionsvia the instruction data output.
 8. The power management unit extendermodule of claim 7, wherein the original software program implements acontrol program for a supply voltage regulator circuit of at least onepoint of load of an electronic system.
 9. The power management unitextender module of claim 7, wherein the microprocessor coupled to themicroprocessor interface is configured to serially receive the addressand command information from a logic block that conforms to an SMBUS.orgprotocol.
 10. The power management unit extender module of claim 7,wherein the memory interface is configured for coupling to a randomaccess memory (RAM) to access the table of jump values, a read onlymemory to access the original software routine, and a rewritablenon-volatile memory to access the substitute software routine.
 11. Thepower management unit extender module of claim 7, wherein the powermanagement jump value is an address and the table of jump values is atable of addresses, and wherein when the comparing logic detects a matchbetween a starting address of the original software routine and a valuein the table of jump values, a starting address of the substitutesoftware routine is loaded into the power management unit extenderprogram counter.
 12. The power management unit extender module of claim7, comprising: a serial interface, the serial interface configured toreceive instructions of the substitute software routine, theinstructions of the substitute software routine storable in memory viathe memory interface, wherein the receipt of instructions of thesubstitute software routine causes the power management unit extendermodule to update the table of jump values to include valuescorresponding to the substitute software routine.
 13. The powermanagement unit extender module of claim 12, comprising: a securitymodule, the security module configured to decrypt data received via theserial interface.
 14. A power management method to control a supplyvoltage regulator circuit of at least one point of load of an electronicsystem, comprising: loading, with a power management extender module, atable of jump values into a first rewritable memory; loading, with thepower management extender module, a substitute software routine into asecond rewritable memory; serially receiving a power managementtransaction with a microprocessor, the power management transactionincluding address value information and command value information;receiving, by the power management extender module, a program counterinput from the microprocessor, the program counter input representingcommencement of a power management command; comparing the programcounter input to at least one value in the table of jump values, andbased on the result of the comparison, performing the acts of: when theprogram counter input matches a value in the table of jump values,loading a power management unit extender program counter with a startaddress of the substitute software routine, sequencing throughinstructions of the substitute software routine wherein the instructionsare passed to the microprocessor for execution, and loading the powermanagement unit extender program counter with a return address; or whenthe program counter input does not match any values in the table of jumpvalues, loading the power management unit extender program counter witha start address of an original software routine.
 15. The powermanagement method of claim 14, wherein the first rewritable memory andthe second rewritable memory are the same non-volatile rewritablememory.
 16. The power management method of claim 14, wherein the powermanagement transaction conforms to an SMBUS.org protocol.
 17. The powermanagement method of claim 16, comprising: detecting the powermanagement transaction; asserting an interrupt to the microprocessor;and in response to the interrupt, passing the program counter inputrepresenting commencement of the power management command to the powermanagement extender module.
 18. The power management method of claim 14,comprising: serially receiving, with the power management extendermodule, instructions of the substitute software routine, theinstructions of the substitute software routine; decrypting theinstructions of the substitute software routine; and updating the tableof jump values to include values corresponding to the substitutesoftware routine.
 19. The power management method of claim 14, whereinthe tables of jump values includes pointers to a plurality of substitutesoftware routines, the plurality of substitute software routinesarranged to increase the number of command routines that are availablefor execution.
 20. The power management method of claim 19, wherein thepointers in the tables of jump values are arranged in cooperative firstpairs and second pairs, a first pair including the program counter inputrepresenting commencement of a power management command and the startaddress of the substitute software routine, a second pair including theend address of the substitute software routine and a return address.